Relaxing and Restraining Queries for OBDA

In ontology-based data access (OBDA), ontologies have been successfully employed for querying possibly unstructured and incomplete data. In this paper, we advocate using ontologies not only to formulate queries and compute their answers, but also for modifying queries by relaxing or restraining them, so that they can retrieve either more or less answers over a given dataset. Towards this goal, we first illustrate that some domain knowledge that could be naturally leveraged in OBDA can be expressed using complex role inclusions (CRI). Queries over ontologies with CRI are not first-order (FO) rewritable in general. We propose an extension of DL-Lite with CRI, and show that conjunctive queries over ontologies in this extension are FO rewritable. Our main contribution is a set of rules to relax and restrain conjunctive queries (CQs). Firstly, we define rules that use the ontology to produce CQs that are relaxations/restrictions over any dataset. Secondly, we introduce a set of data-driven rules, that leverage patterns in the current dataset, to obtain more fine-grained relaxations and restrictions

Sustainable tourism perspective to strengthen competitive tourism destination

In the last decades tourism sector has seen a significant growth. Despite a plethora of cultural and financial benefits, such boisterous tourism development might bring a lot of negative consequences for the whole tourism locality. Eventually, there arose a strong need to regulate this development in such a way which would bring as much harm as possible. Nowadays, harmonious tourism is seen as a priority for the majority of tourist attractions. According to World Tourism Organisation, in the long run the competitive ability of any tourist locality depends on harmony. The goal of this research is to determine and investigate the main factors which influence the competitive ability of tourist locality as well as the interplay of these factors through the perspective of harmonious tourism. To achieve the goal, the town of Anykščiai has been chosen as a tourist locality for the research. Both qualitative and quantitative methods have been used in the research. During the process of the qualitative research, a specialist of the Anykščiai tourism information centre was interrogated. The quantitative research method included 17 members of the Anykščiai tourism clusters. During the process of the research, the interplay of the competitive ability between harmonious tourism and tourist localities has been established. This interplay is manifested through the external and internal factors of the competitive ability of tourist localities. Those tourist localities which pursue the development of harmonious tourism have to follow the recommendations proposed by World Tourism Organization as well as the criteria of the Universal Board of Harmonious Tourism. The accomplishment of these criteria in the town of Anykščiai displayed a positive influence on the internal factors of the competitive ability of the tourist locality

Well-founded Semantics for Recursive SHACL

W3C has recently introduced SHACL as a new standard for integrity constraints on RDF graphs. Unfortunately, the standard defines the semantics of non-recursive constraints only, which has spurred recent research efforts into finding a suitable, mathematically crisp semantics for constraints with cyclic dependencies. To this end, Corman et al. [1] introduced a semantics related to supported models known in logic programming, while Andresel et al. [2] presented a semantics based on stable models known in Answer Set Programming (ASP). In this paper, we argue that recursive SHACL can be naturally equipped with a semantics inspired in the well-founded semantics for (recursive) DATALOG queries with default negation. This semantics is not only intuitive, but it is also computationally tractable, unlike the previous proposals. To draw a connection with the classic definition of well-founded semantics in logic programming, we provide a simple translation of recursive SHACL under the well-founded semantics into propositional logic programs under the well-founded semantics. This translation is not only of theoretical interest: It can be efficiently implemented using the functionality of standard RDF triple stores (specifically, by issuing a small number of SPARQL queries), followed by an efficient evaluation using an existing engine for computing the well-founded model of a propositional logic program

Lietuvos bankų paskolų pasiskirstymas pagal ekonominę veiklą finansinio stabilumo požiūriu

The article examines the influence of distribution of Lithuanian banks’ loans against the economic activities on the country’s financial stability during the time period of 2000-2006. By applying the methods of mathematical statistics and econometrical analysis of time lines, the changes of the indicators of concentration of loan portfolios and the distance measurements in relation with time are evaluated. The obtained results are interpreted in the aspects of diversification of loan portfolios and financial stability. The article comes up to the conclusion that the loan portfolios of most of the country’s banks in the second quarter of the 2006 became more diversified than at the end of 1999 therefore the sensitivity of the banks reduced upon interruption of one economic activity. On the other hand the probability that the interruptions of economic activities of several types could have influenced most of the country’s banks simultaneously has increased. The sensitivity of Lithuanian banks to the changes in the crediting of real estate especially increased with the growth of the activity

Well-founded Semantics for Recursive SHACL

W3C has recently introduced SHACL as a new standard for integrity constraints on RDF graphs. Unfortunately, the standard defines the semantics of non-recursive constraints only, which has spurred recent research efforts into finding a suitable, mathematically crisp semantics for constraints with cyclic dependencies. To this end, Corman et al. [1] introduced a semantics related to supported models known in logic programming, while Andresel et al. [2] presented a semantics based on stable models known in Answer Set Programming (ASP). In this paper, we argue that recursive SHACL can be naturally equipped with a semantics inspired in the well-founded semantics for (recursive) DATALOG queries with default negation. This semantics is not only intuitive, but it is also computationally tractable, unlike the previous proposals. To draw a connection with the classic definition of well-founded semantics in logic programming, we provide a simple translation of recursive SHACL under the well-founded semantics into propositional logic programs under the well-founded semantics. This translation is not only of theoretical interest: It can be efficiently implemented using the functionality of standard RDF triple stores (specifically, by issuing a small number of SPARQL queries), followed by an efficient evaluation using an existing engine for computing the well-founded model of a propositional logic program

Semantic querying of integrated raster and relational data : a virtual knowledge graph approach

Ontology-based data access (OBDA) facilitates access to heterogeneous data sources through the mediation of an ontology (e.g. OWL), which captures the domain of interest and is connected to data sources through a declarative mapping. In our study, large, heterogeneous earth observational (EO) data, known as raster data, and geometrical data, known as vector data, are considered as (heterogeneous) data sources. Raster data represent, e.g., Earth's natural phenomena, such as surface temperature, elevation, or air pollution, as multidimensional arrays. In contrast, vector data depict, e.g., locations, networks, or regions on Earth, using geometries. Domain experts, such as earth scientists and GIS practitioners, still struggle to undertake advanced studies by querying large raster and vector data in an integrated way because, unlike relational data, they come in diverse formats and different data structures. In our approach to integration, we use a geospatial extension of an RDBMS to represent vector data as relational data, and a domain-agnostic array DBMS to handle raster data. Our aim is to extend the OBDA paradigm to effectively deal with relational, vector, and raster data in a combined way, while leveraging the built-in capabilities of data management tools relevant to each type of data. We also plan to develop techniques to calculate on the fly for each user query posed over the ontology an optimal query plan that exploits, at best, the query processing capabilities of each tool, while limiting costly data transfer operations between tools

On the expressive power of ontology-mediated queries : capturing coNP

The complexity and relative expressiveness of Ontology-mediated Queries (OMQs) is quite well understood by now. In this paper, we study the expressive power of OMQs from a descriptive complexity perspective, where the central question is to understand whether a given OMQ language is powerful enough to express all queries that can be computed within some bound on time or space. We show that the OMQ language that pairs instance queries with ontologies in the very expressive DL ALCHOI with closed predicates cannot express all coNP-computable Boolean queries, despite being coNP-complete in data complexity. We, then, propose an extension of this OMQ language that is expressive enough to precisely capture the class of all Boolean queries computable in coNP. This involves adding functionality as well as path expressions and nominal schemata, which are restricted in a way that allows us to carefully incorporate them into the existing mosaic technique for the DL ALCHOIF with closed predicates without affecting the coNP upper bound in data complexity